path: root/qtools/qptrdict.doc

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/*****************************************************************************
  QPtrDict documentation
 *****************************************************************************/

/*!
  \class QPtrDict qptrdict.h
  \brief The QPtrDict class is a template class that provides a dictionary based on \c void* keys.

  \ingroup collection
  \ingroup tools

  QPtrDict is implemented as a template class. Define a
  template instance QPtrDict\<X\> to create a dictionary that operates on
  pointers to X, or X*.

  A dictionary is a collection that associates an item with a key.
  The key is used for inserting and looking up an item.  QPtrDict has
  \c void* keys.

  The dictionary has very fast insertion and lookup.

  Example:
  \code
    #include <qptrdict.h>
    #include <stdio.h>

    void main()
    {
	int *a = new int[12];
	int *b = new int[10];
	int *c = new int[18];
	int *d = new int[13];

	QPtrDict<char> dict;		   // maps void* -> char*

	dict.insert( a, "a is int[12]" );  // describe pointers
	dict.insert( b, "b is int[10]" );
	dict.insert( c, "c is int[18]" );

	printf( "%s\n", dict[a] );	   // print descriptions
	printf( "%s\n", dict[b] );
	printf( "%s\n", dict[c] );

	if ( !dict[d] )
	    printf( "d not in dictionary\n" );
    }
  \endcode

  Program output:
  \code
	a is int[12]
	b is int[10]
	c is int[18]
	d not in dictionary
  \endcode

  The dictionary in our example maps \c int* keys to \c char* items.
  QPtrDict implements the \link operator[] [] operator\endlink to lookup
  an item.

  QPtrDict is implemented by QGDict as a hash array with a fixed number of
  entries. Each array entry points to a singly linked list of buckets, in
  which the dictionary items are stored.

  When an item is inserted with a key, the key is converted (hashed) to
  an integer index into the hash array using the \c mod operation. The
  item is inserted before the first bucket in the list of buckets.

  Looking up an item is normally very fast. The key is again hashed to an
  array index. Then QPtrDict scans the list of buckets and returns the item
  found or null if the item was not found.  You cannot insert null pointers
  into a dictionary.

  The size of the hash array is very important. In order to get good
  performance, you should use a suitably large \link primes.html prime
  number\endlink.  Suitable means equal to or larger than the maximum
  expected number of dictionary items.

  Items with equal keys are allowed.  When inserting two items with the
  same key, only the last inserted item will be visible (last in, first out)
  until it is removed.

  Example:
  \code
    #include <qptrdict.h>
    #include <stdio.h>

    void main()
    {
	QPtrDict<char> dict;		// maps char* ==> char*

	double *ptr = new double[28];
	dict.insert( ptr, "first" );
	dict.insert( ptr, "second" );

	printf( "%s\n", dict[ptr] );
	dict.remove( ptr );
	printf( "%s\n", dict[ptr] );
    }
  \endcode

  Program output:
  \code
	second
	first
  \endcode

  The QPtrDictIterator class can traverse the dictionary contents, but only
  in an arbitrary order.  Multiple iterators may independently traverse the
  same dictionary.

  Calling setAutoDelete(TRUE) for a dictionary tells it to delete items
  that are removed .  The default is to not delete items when they are
  removed.

  When inserting an item into a dictionary, only the pointer is copied, not
  the item itself. This is called a shallow copy. It is possible to make the
  dictionary copy all of the item's data (known as a deep copy) when an
  item is inserted.  insert() calls the virtual function
  QCollection::newItem() for the item to be inserted.
  Inherit a dictionary and reimplement it if you want deep copies.

  When removing a dictionary item, the virtual function
  QCollection::deleteItem() is called.  QPtrDict's default implementation
  is to delete the item if auto-deletion is enabled.

  \sa QPtrDictIterator, QDict, QAsciiDict, QIntDict,
      \link collection.html Collection Classes\endlink
*/


/*!
  \fn QPtrDict::QPtrDict( int size )
  Constructs a dictionary using an internal hash array with the size
  \e size.

  Setting \e size to a suitably large \link primes.html prime number\endlink
  (equal to or greater than the expected number of entries) makes the hash
  distribution better and hence the loopup faster.
*/

/*!
  \fn QPtrDict::QPtrDict( const QPtrDict<type> &dict )
  Constructs a copy of \e dict.

  Each item in \e dict are inserted into this dictionary.
  Only the pointers are copied (shallow copy).
*/

/*!
  \fn QPtrDict::~QPtrDict()
  Removes all items from the dictionary and destroys it.

  All iterators that access this dictionary will be reset.

  \sa setAutoDelete()
*/

/*!
  \fn QPtrDict<type> &QPtrDict::operator=(const QPtrDict<type> &dict)
  Assigns \e dict to this dictionary and returns a reference to this
  dictionary.

  This dictionary is first cleared, then each item in \e dict is inserted
  into this dictionary.
  Only the pointers are copied (shallow copy), unless newItem() has been
  reimplemented().
*/

/*!
  \fn uint QPtrDict::count() const
  Returns the number of items in the dictionary.
  \sa isEmpty()
*/

/*!
  \fn uint QPtrDict::size() const
  Returns the size of the internal hash array (as specified in the
  constructor).
  \sa count()
*/

/*!
  \fn void QPtrDict::resize( uint newsize )
  Changes the size of the hashtable the \a newsize.
  The contents of the dictionary are preserved,
  but all iterators on the dictionary become invalid.
*/

/*!
  \fn bool QPtrDict::isEmpty() const
  Returns TRUE if the dictionary is empty, i.e. count() == 0. Returns FALSE
  otherwise.
  \sa count()
*/

/*!
  \fn void QPtrDict::insert( void *key, const type *item )
  Inserts the \e key with the \e item into the dictionary.

  The key does not have to be a unique dictionary key.  If multiple items
  are inserted with the same key, only the last item will be visible.

  Null items are not allowed.

  \sa replace()
*/

/*!
  \fn void QPtrDict::replace( void *key, const type *item )
  Replaces an item which has a key equal to \e key with \e item.

  If the item does not already exist, it will be inserted.

  Null items are not allowed.

  Equivalent to:
  \code
    QPtrDict<char> dict;
	...
    if ( dict.find(key) )
	dict.remove( key );
    dict.insert( key, item );
  \endcode

  If there are two or more items with equal keys, then the last inserted
  of these will be replaced.

  \sa insert()
*/

/*!
  \fn bool QPtrDict::remove( void *key )
  Removes the item associated with \e key from the dictionary.
  Returns TRUE if successful, or FALSE if the key does not exist in the
  dictionary.

  If there are two or more items with equal keys, then the last inserted
  of these will be removed.

  The removed item is deleted if \link QCollection::setAutoDelete()
  auto-deletion\endlink is enabled.

  All dictionary iterators that refer to the removed item will be set to
  point to the next item in the dictionary traversing order.

  \sa take(), clear(), setAutoDelete()
*/

/*!
  \fn type *QPtrDict::take( void *key )
  Takes the item associated with \e key out of the dictionary without
  deleting it (even if \link QCollection::setAutoDelete()
  auto-deletion\endlink is enabled).

  If there are two or more items with equal keys, then the last inserted
  of these will be taken.

  Returns a pointer to the item taken out, or null if the key does not
  exist in the dictionary.

  All dictionary iterators that refer to the taken item will be set to
  point to the next item in the dictionary traversing order.

  \sa remove(), clear(), setAutoDelete()
*/

/*!
  \fn void QPtrDict::clear()
  Removes all items from the dictionary.

  The removed items are deleted if \link QCollection::setAutoDelete()
  auto-deletion\endlink is enabled.

  All dictionary iterators that access this dictionary will be reset.

  \sa remove(), take(), setAutoDelete()
*/

/*!
  \fn type *QPtrDict::find( void *key ) const
  Returns the item associated with \e key, or null if the key does not
  exist in the dictionary.

  This function uses an internal hashing algorithm to optimize lookup.

  If there are two or more items with equal keys, then the last inserted
  of these will be found.

  Equivalent to the [] operator.

  \sa operator[]()
*/

/*!
  \fn type *QPtrDict::operator[]( void *key ) const
  Returns the item associated with \e key, or null if the key does not
  exist in the dictionary.

  This function uses an internal hashing algorithm to optimize lookup.

  If there are two or more items with equal keys, then the last inserted
  of these will be found.

  Equivalent to the find() function.

  \sa find()
*/

/*!
  \fn void QPtrDict::statistics() const
  Debugging-only function that prints out the dictionary distribution
  using qDebug().
*/


/*****************************************************************************
  QPtrDictIterator documentation
 *****************************************************************************/

/*!
  \class QPtrDictIterator qptrdict.h
  \brief The QPtrDictIterator class provides an iterator for QPtrDict collections.

  \ingroup collection
  \ingroup tools

  QPtrDictIterator is implemented as a template class.
  Define a template instance QPtrDictIterator\<X\> to create a
  dictionary iterator that operates on QPtrDict\<X\> (dictionary of X*).

  Example:
  \code
    #include <qptrdict.h>
    #include <stdio.h>

    void main()
    {
	int *a = new int[12];
	int *b = new int[10];
	int *c = new int[18];
	int *d = new int[13];

	QPtrDict<char> dict;		   // maps void* -> char*

	dict.insert( a, "a is int[12]" );  // describe pointers
	dict.insert( b, "b is int[10]" );
	dict.insert( c, "c is int[18]" );

	QPtrDictIterator<char> it( dict ); // iterator for dict

        while ( it.current() ) {
	    printf( "%x -> %s\n", it.currentKey(), it.current() );
	    ++it;
	}
    }
  \endcode

  Program output:
  \code
	804a788 -> a is int[12]
	804a7f0 -> c is int[18]
	804a7c0 -> b is int[10]
  \endcode

  Note that the traversal order is arbitrary, you are not guaranteed the
  order above.

  Multiple iterators may independently traverse the same dictionary.
  A QPtrDict knows about all iterators that are operating on the dictionary.
  When an item is removed from the dictionary, QPtrDict update all
  iterators that are referring the removed item to point to the next item
  in the traversing order.

  \sa QPtrDict, \link collection.html Collection Classes\endlink
*/

/*!
  \fn QPtrDictIterator::QPtrDictIterator( const QPtrDict<type> &dict )
  Constructs an iterator for \e dict.  The current iterator item is
  set to point on the first item in the \e dict.
*/

/*!
  \fn QPtrDictIterator::~QPtrDictIterator()
  Destroys the iterator.
*/

/*!
  \fn uint QPtrDictIterator::count() const
  Returns the number of items in the dictionary this iterator operates on.
  \sa isEmpty()
*/

/*!
  \fn bool QPtrDictIterator::isEmpty() const
  Returns TRUE if the dictionary is empty, i.e. count() == 0. Returns FALSE
  otherwise.
  \sa count()
*/

/*!
  \fn type *QPtrDictIterator::toFirst()
  Sets the current iterator item to point to the first item in the
  dictionary and returns a pointer to the item.
  If the dictionary is  empty it sets the current item to null and 
  returns null.
*/

/*!
  \fn QPtrDictIterator::operator type *() const
  Cast operator. Returns a pointer to the current iterator item.
  Same as current().
*/

/*!
  \fn type *QPtrDictIterator::current() const
  Returns a pointer to the current iterator item.
*/

/*!
  \fn void *QPtrDictIterator::currentKey() const
  Returns the key for the current iterator item.
*/

/*!
  \fn type *QPtrDictIterator::operator()()
  Makes the succeeding item current and returns the original current item.

  If the current iterator item was the last item in the dictionary or if it
  was null, null is returned.
*/

/*!
  \fn type *QPtrDictIterator::operator++()
  Prefix ++ makes the succeeding item current and returns the new current
  item.

  If the current iterator item was the last item in the dictionary or if it
  was null, null is returned.
*/

/*!
  \fn type *QPtrDictIterator::operator+=( uint jump )
  Sets the current item to the item \e jump positions after the current item,
  and returns a pointer to that item.

  If that item is beyond the last item or if the dictionary is  empty,
  it sets the current item to null and returns null.
*/